1. Field of the Invention
The present invention relates to a linear motion guide unit in which separating elements are each arranged between any adjoining rolling elements running along a circulating endless passages.
2. Description of the Prior Art
Conventionally a linear motion guide unit shown in FIG. 10 is well known to those skilled in the art.
The prior linear motion guide unit comprises an elongated track rail 2 having raceway grooves 4 on lengthwise side surfaces thereof, and a sliding element, or a slider 1, saddling on a track rail 2 so as to freely move along and with respect to the track rail 2 and having raceway grooves 9 confronting the raceway grooves 4 of the track rail 1. The slider 1 moves along the track rail 1 by virtue of rolling elements, or balls 7, running through raceways 16 defined between the confronting raceway grooves 4, 9. The track rail 2 has openings 13 boring through from an upper surface to a bottom surface thereof at locations spaced lengthwise from each other. The track rail 2 may be fixed together with the mounting base 20, such as a bed, machine base, work table or the like, by screwing bolts through the openings 13 of the track rail 2 and openings in the mounting base 15.
The slider 1 has a casing 5 movable relatively to the track rail 2, and end caps 6 secured to the opposing ends of the casing 5. Provided on the upper surface of the casing 5 are openings 19 for mounting the slider 1 to other appliances, parts, chucks, grasping jaws or the like. The end caps 6 are attached on the lengthwise opposing end surfaces of the casing 5 by means of bolts 25. Both of casing 5 and the end caps 6 are formed on the lower surfaces thereof with recesses 10 by which the casing 5 and end caps 6 may saddle on track rail 2 for free movement. The casing is provided with return passages 12 extending in parallel with the raceway grooves 9. The end caps 6 are provided with claws for scooping the balls 7 out of the raceways 16 defined between the confronting raceway grooves 4, 9 and turnaround passages, shown at 15 in FIG. 2, for endless circulation of the balls 7.
In the linear motion guide unit described above, retainer bands 18 are provided in the casing 5 so as to hold the balls 7 to thereby prevent the balls 7 from falling out of the casing 5. Bottom seals 8 are secured to the lower surfaces of the casing 5 and the end caps 6 to thereby for close clearances between the track rail 2 and the slider 1. Mounted on the end caps 6 are end seals 17 for keeping sealing function between the track rail 2 and the lengthwise opposing ends of slider 1.
The balls 7 run along the load areas, that is, the raceway 18 defined between the raceway grooves 4 of the track rail 2 and the raceway grooves 9 of the casing 5, and then come in the turnaround passages 15 in any one of the end caps 6. The balls 7 further run from the turnaround passages 15 to the return passages 12 that are formed in the casing 5 in parallel with the raceway grooves 9. Subsequently the balls 7 return to the loaded areas of the raceways 16 through the turnaround passages 15 in the other one of the end caps 6. It will be thus understood that the balls 7 may run in a circulating manner though the raceways 16, turnaround passages, shown at 21 in FIG. 2, and return passages 12, causing the smooth movement of the slider 1 relatively to the track rail 2. Lubricant may be supplied through grease nipples 11 into the casing 5 so as to lubricate the raceway grooves 4, 9 along which run the balls 7.
Disclosed in Japanese Utility Model Laid-Open No. 178659/1988 is a machine element for smoothly transmitting torque by virtue of circulation of the balls. The machine element includes therein members that are arranged between the adjoining balls so as to convert the contact relation of the adjoining balls from direct rolling-contact relation to line-contact or area-contact relation to thereby reduce the contact stress so that clearances between the adjoining balls may be ensured for the provision of the lubricant films or for retaining the lubricant therein. The members interposed between any two adjoining rolling elements are usually formed in a cylinder and are apt to be worn away. In such machine element as described above, there are adverse possibilities in which the worn members may stumble along the raceways, resulting in being caught between the raceway grooves and the balls and in which the worn members may fall off from the slider.
Separators for ball bearings are disclosed in Japanese Patent Publication No. 24405/1965, wherein the separators are interposed between any adjoining balls, the separators being each comprised of a cylinder and a web that is designed so as to make contact with the adjacent webs of the separators whereby the webs may directly transmit to each other the force acting on the separators in the rotating direction of the ball bearing. On such separators of the ball bearings, the webs are formed so as to make contact with each other and, therefore, the curvature of the bearing is inevitably fixed in radius.
Moreover another linear motion rolling bearing disclosed in Japanese Patent Laid-Open No. 242126/1987, wherein there are provided retainer bands for keeping in position rolling elements, the retainers being each provided with openings to hold the rolling elements therein with a small clearance apart, and further formed with annular thin ridges around the openings to keep the balls against falling off the bearing. Nevertheless, the retainer band, when being damaged at a location, at least, should be entirely replaced with new one.
Further, a chain of balls disclosed in Japanese Patent Laid-Open No. 52217/1993 comprises ball retainers each interposed between any adjoining two balls that are arranged in series, and a flexible elongated member for connecting together the balls and retainers in a tandem array. The ball chain may be bent in an endless form. The ball chain has been be produced by the steps of forming the retainers and connecting members integrally by the injection molding, and then inserting the balls in the mold to thereby finish the integrated product with the balls. This integrated molding of the retainers with the connecting members by injection molding disadvantageously renders the molding machines and molds large-scaled and production works much more difficult. In addition, the ball chain, when being damaged at a location, at least, should be entirely replaced with new one.
Meantime the linear motion guide unit shown in FIG. 10 is a ball-rolling type in which balls 7 run in an endless circulation with making contact with each other. Such ball-rolling type guide units are of various types and also presently availed in extended fields.
The linear motion guide units are recently required more and more to deal with the low noise, maintenance-free design and high-speed operation. Nevertheless, presently available ball-rolling type guide units scarcely render the requirements satisfactory because the balls make metal-contact to thereby cause the reaction at the direct contact, resulting in generating noise.